1. Field of the Disclosure
The present disclosure relates to a thermocouple and a manufacturing method for same.
2. Discussion of the Background Art
In recent years, with regard to power semiconductors, glasses, and oxide single crystals of other laser elements, piezo elements, scintillator elements, or the like, performance improvement is required and a manufacturing temperature tends to increase. In addition, even with regard to an engine combustion temperature in a field of aerospace, performance improvement is required and a manufacturing temperature tends to increase. In a high temperature field of 1500° C. or higher, a radiation thermometer can be used for temperature measurement in general. In the temperature measurement using the radiation thermometer, energy of infrared light and visible light is measured in response to a temperature of an object and is converted into a temperature. For this reason, in the radiation thermometer, a temperature of a surrounding environment (particularly, in a case where water vapor, dust, gas, or the like is present) or a space itself cannot be measured in principle. Accordingly, there was a problem that the temperature could not be precisely measured.
A thermocouple is a stable temperature sensor with high accuracy using a Seebeck effect. However, the thermocouple cannot be stably used under a severe environment such as an oxidation atmosphere or a carbon-reducing atmosphere in the high temperature field of 1500° C. or higher and relies on calculation values by combustion gas analysis or a temperature simulation obtained from a heating output.
The cause that the thermocouple cannot be stably used under the oxidation atmosphere or the carbon-reducing atmosphere is associated with element wires and a protective tube, and an insulator provided therebetween. A thermocouple to be used at a high temperature is, for example, a thermocouple having element wires which are formed using Pt and Rh, a thermocouple having element wires which are formed using Ir and Rh, or a thermocouple having element wires which are formed using W and Re. The thermocouple having the element wires formed using Pt and Rh is vulnerable to the carbon-reducing atmosphere. The thermocouple having the element wires formed using W or Re cannot be used, resulting from oxidation damage in the oxidation atmosphere. In addition, the thermocouple having the element wires formed using Ir and Rh has durability in both environments compared to other thermocouples, but the durability is not satisfactory. Thus, a protective tube is used. For example, there is disclosed a thermocouple in which metal element wires constituting a temperature measurement junction in such a manner that ends at one side thereof are joined to each other and being made up of one pair out of a pair of Pt—Rh alloy wire and Pt—Rh alloy wire, a pair of Pt wire and Pt—Rh alloy wire, and a pair of Ir wire and Ir—Rh alloy wire are inserted into an insulating tube, the insulating tube is inserted into a protective tube, and a filler is filled in a gap between the protective tube and the element wires (for example, see Patent Literature 1). In addition, there is disclosed a thermocouple in which element wires coated with colloidal silica is inserted into a protective tube made of alumina or a protective tube made of quartz (for example, see Patent Literature 2).
Although it is not a thermocouple technology, as a method for suppressing volatilization loss of platinum-group noble metals constituting a high-temperature apparatus, there is disclosed a method for forming a coating layer having a thickness of 50 to 500 μm and made of stabilized zirconia on an outer surface of the high-temperature apparatus by spraying (for example, see Patent Literature 3).
A manufacturing method for a sheathed thermocouple is disclosed (for example, see Patent Literature 4).